Steady-state characteristics of a continuous-flow photobioreactor for neutral lipids synthesis by microalgae

Abstract

Abstract The paper presents a mathematical model of a continuous-flow bioreactor in which cultivation of Pseudochlorococcum sp. algae proceeds. The process is directed on synthesis of neutral lipids, which are used for production of third-generation biodiesel. The model takes into account influence of light and nutrient limitation on the growth of microalgae. Numerical simulations were performed in order to determine steady-state properties of the bioreactor. The influence of key process parameters was investigated and detailed process interpretation was presented. Existence of optimal dilution rate and optimal influent nitrogen concentration was proved. In order to obtain maximum lipids productivity, lower dilution rate is required for higher influent inorganic nitrogen concentration. The factor limiting the process changes with the increase in the dilution rate. At low dilution rates the process is limited by nitrogen. At intermediate dilution rates the process is limited by light, whereas at high dilution rates the process is once again limited by nitrogen. Existence of a critical irradiance below which the biomass wash-out occurs was shown. The results presented are both of cognitive and practical importance.